1. Field of the Invention
The present invention is related to an internal liner inserted between the lower part of the leg and the foot of a skier and a shell of a sports boot such as an alpine ski boot, such liner comprising a vamp enveloping the foot which is overlaid by an upper enveloping the lower part of the leg and constituted by a rear portion and a front portion respectively forming a rear wedge and a front wedge, that are joined to constitute a wall having a given thickness, adapted to play an adjustment role for the footwear between the internal surface of the shell of the boot and the lower part of the leg.
2. Discussion of Background and Relevant Information
Liners of the above-mentioned type are known, the walls thereof, especially the walls of the upper, being constituted of an elastic material, for example, polyurethane, providing a certain general comfort, but whose main disadvantage lies in the fact that it requires the provision of a covering tongue of an opening for entry of the foot.
Such a tongue not only complicates the manufacture of the liner itself, but in addition, runs the risk of constituting an excess thickness by lateral sliding during skiing and thus creating compression points that are incompatible with the comfort desired.
To overcome this disadvantage, French Patent Publication No. 2,360,271 discloses an internal liner whose ascending upper is closed along its entire periphery, and has greater circumferential stretching ability than the other portions.
For this, the wall is divided into strips which extend transversely with respect to the circumference and which are alternately contiguous, like an accordion.
Thus, the liner can expand to enable passage of the foot by a deployment of the accordion-shaped strips forming a type of bellows.
Such a design, however, has a number of disadvantages because by stretching the strips, the thickness of the wall of the liner is varied, and in addition, the wall is provided with a flexibility which is not forcibly desired, especially at the rear portion of the liner which should constitute a firm support against the shell of the boot.
Moreover, this deployment of the strips causes an effect which runs counter to the corpulence of the skier. Indeed, if the skier is heavy, he or she would tend to cause the stretching of the accordion-shaped strips and as such, reduce their resistance, whereas under such circumstances, it would be preferable to reinforce such resistance, and vice versa.
Further, such a design implies use of a material having the same nature. However, experience has proved that a liner that is both comfortable and efficient during skiing should enable a relatively firm rear support as well as a front support in flexion, as per the degree of flexibility selected in accordance with the comfort desired.
Other boots are also known whose internal are liners made of polyurethane and which have, on their external surfaces at least, projections enabling one to determine, in accordance with their number, the portions of the liner whose degree of flexibility is differentiated. French Patent Publication No. 2,336,892 describes a liner of this type. According to this document, the differentiation in flexibility, without however changing the density of the polyurethane which constitutes the wall of the liner, aims at enabling certain portions of the liner to bear different tensions and/or to transmit such tensions differently to the external shell of the boot. As is clear, since the liner is obtained in a single piece including the projections, its adaptation to the foot of the skier occurs due to the flexibility from an initial fitting volume, determined for a foot size. Thus, for a foot that is relatively small in volume, the wall of the liner is not stretched or is only slightly stretched, even in the projections area, thus causing a variation in the flexibility and initial firmness of all the liner portions, whether or not they are provided with projections. It should be noted in this regard that the stretching of the wall does not cause a lessening of the flexibility thereof, but increases its resistance to compressibility, which would appear to be satisfactory. However, due to the fact that there is no exact correlation between, on the one hand, the corpulence, the weight and/or the strength of the skier and, on the other hand, the volume of the feet of the skier, this increase in resistance to compressibility of the wall can be excessive or inadequate.